Key packages brought forth by the Ubuntu 11.04 Alpha 2 release is Libreoffice 3.3, X.Org Server 1.10, Mesa 7.10, Python 2.7, and the Linux 2.6.38-rc2 kernel.
Canonical's Unity Desktop is also used by Ubuntu 11.04 Alpha 2 but the desktop and overall experience is far from being finished. Unity is still a very active work in progress.
There's also Ubuntu Netbook improvements for ARM, ratings and reviews support within the Ubuntu Software Center, better provisioning support on the Ubuntu Server side with the cobbler and mcollective tools, and the Ubuntu EC2 11.04 images now support new Amazon EC2 instance types.
See our Amazon EC2 cloud benchmarks to see how the different Elastic Compute Cloud instances perform with t1.micro, m1.small, and c1.medium instances now working on Ubuntu.
When it comes to Kubuntu 11.04 Alpha 2, the KDE variant of Ubuntu, UDisks and UPower has now replaced HAL, there's the GTK Oxygen theme, KDE Games are now included on the CD, there's a Phonon G-Streamer back-end, and the entire KDE stack has been upgraded against the new KDE Software Collection 4.6 packages. The Xfce version, Xubuntu, has also been upgraded against the Xfce 4.8 desktop.
Canonical's Kate Stewart made the release announcement while more information is to be found on this Ubuntu page with the download links.